In-depth study on the effect of oxygen-containing functional groups in pyrolysis oil by P-31 NMR

Abstract

Both aliphatic and carboxylic OH undergo the same decomposition pathway to form water during in situ31P NMR monitoring.

Factors Affecting the Sensitivity of Hydroxyl Group Content Analysis of Biocrude Products via Phosphitylation and 31P NMR Spectroscopy

“…Comparison of concentrations can be made by considering the strength of this signal, which reveals that sample (matrix) water content decreases in the following order: FP > BC > AM. , Supporting this observation, sample matrix water content, determined independently by Karl Fischer titrimetry, was found to be 18.31 wt % for FP, 2.83 wt % for BC, and <1% for AM. However, as suggested by Wu, the intensity of the signal at 133 ppm may reflect not only sample water content but also O­(PO 2 C 6 H 12 ) 2 generated by the decomposition of unstable phosphitylated intermediates …”

“…These measured concentrations were then plotted against the actual concentrations, determined from measured masses (grams) of model compounds added during sample preparation. The samples were analyzed by 31 P NMR spectroscopy within ∼30 min after the addition of TMDP and Pyr, as suggested by previous reports stating that the phosphitylated derivatives, particularly those derived from carboxylic acids, are unstable in the reaction solution. , Wu stated that the phosphitylated carboxylic acid population could degrade by as much as 30% in 4 h after reaction with TMDP …”

“…The phosphitylation reaction replaces hydroxyl protons with the dioxaphospholane moiety at the hydroxyl O atom, giving rise to 31 P signals with chemical shifts that differ from that of TMDP. Since the phosphitylation reaction occurs rapidly, the sample was analyzed within 30 min following the addition of TMDP, as prescribed by Wu …”

“…Since the phosphitylation reaction occurs rapidly, the sample was analyzed within 30 min following the addition of TMDP, as prescribed by Wu. 50 2.3. NMR Data Acquisition and Processing.…”

“…However, as suggested by Wu, the intensity of the signal at 133 ppm may reflect not only sample water content but also O(PO 2 C 6 H 12 ) 2 generated by the decomposition of unstable phosphitylated intermediates. 50 The TMDP hydrolysis product, O(PO 2 C 6 H 12 ) 2 , has limited solubility in the reaction mixture. If too much of this product is present in a sample, its precipitation may impede NMR magnetic field homogeneity, distorting 31 P signals (even after optimization through shimming) and thereby precluding accurate measurement of signal intensities.…”